Flexible catheters which are advanced through arteries or veins are used for intravascular or intracardial treatment. At the tip or side of said catheters functional mechanisms are provided, for example to stimulate or cauterize tissue or to conduct electrical signals. In order to be able to deliver the catheter to the correct positions in the cardiac or vascular system, the catheters have to be moved and guided by the physician. Such guidance has to be precise, fast and highly flexible, in particular because the vascular system is a convoluted system that contains a number of bends. Most of the time during treatment is taken up by the navigation of the catheter. Catheters of this kind are conventionally steered solely by manipulating the end that projects out of the patient. By rotating, pushing forward and retracting the catheter, said actions being observed through X-ray monitoring, in combination with a curvature in the tip of the catheter, the catheter tip is caused to take the desired route, which the rest of the catheter then follows. A catheter of this kind moved by the user has to be relatively stiff so that movements can be reliably continued also when negotiating bends. This runs counter to safety requirements, however, since a stiff catheter is more likely to cause injuries.